Since instant noodles are extremely low in moisture content and are in a dry state, they excel in long-term storage. In addition, the instant noodles can be reconstituted and eaten only by immersing the instant noodles in boiling water and leaving them for several minutes or by boiling the instant noodles in boiling water for about one to several minutes. Thus, the instant noodles are extremely convenient food products.
Generally, the instant noodles are produced such that: a noodle dough is prepared using cereal flour, such as wheat flour, as a main raw material; the dough is rolled out and cut to produce raw noodle strings; raw noodles strings are steamed or boiled, i.e., subjected to a gelatinization process; the noodle strings are cut into one meal amount; and the noodle strings are dried (moisture of the noodle strings are removed). Depending on the type of this drying step, the instant noodles are classified broadly into fried noodles and non-fried noodles. The fried noodles are noodles produced by frying the gelatinized noodles in oil having a high temperature of about 150° C. to dry the noodles. In contrast, the non-fried noodles are noodles produced by drying the gelatinized noodles by a method, such as hot-air drying, microwave irradiation, low-temperature air drying, or freeze dry, other than the frying process.
In the gelatinization process before the drying step, starch is changed into an easily digestible form, i.e., α-starch by a water-adding and heating process. The starch contained in cereals, such as wheat flour, is called β-starch, and the β-starch is hardly acted upon by a digestive enzyme and hardly digested. However, by adding water to the β-starch and heating it, its molecular structure breaks and paste-like gelatinized starch (α-starch) is produced. The α-starch is easily acted upon by the digestive enzyme and easily digested. It is known that the gelatinization process significantly influences the quality of noodles to be eaten (see NPL 1 for example).
In the gelatinization process of the instant noodles, normally, steam generated by a boiler is introduced to a steam chamber, and the noodle strings are steamed by this steam. Generally, the cut raw noodles strings are steamed by saturated steam at a temperature close to the boiling point of water. Moreover, it is known that the gelatinization process of the raw noodles is carried out by not the saturated steam but the superheated steam (see PTL 1 and PTL 2 for example). The superheated steam is steam generated by forcibly increasing the temperature of the saturated steam to 100° C. or higher under atmospheric pressure.
PTL 1 describes that steamed noodles having viscoelasticity are obtained by carrying out steaming for a comparatively long period of time using the superheated steam in the gelatinization process of the raw noodles, but does not describe the evaluation of the instant noodles. PTL 2 describes that the raw noodles having high moisture content are gelatinized and dried by the superheated steam and a moisture evaporation rate of the fresh noodles at this time is adjusted to obtain dried noodles which are uniformly swelled without cracks or blisters.
However, a known problem is that in the case of carrying out the gelatinization process of the noodle strings using the superheated steam, due to high heat amount of the superheated steam, a drying rate becomes higher than a gelatinization rate, the gelatinization does not adequately proceed up to a center portion of each noodle string, and the quality of the noodle becomes low in smoothness. Further, to solve this problem, in a case where moisture is supplied to the noodle strings which are being steamed in a steamer, the noodle strings are steamed well. However, a known problem is that since the noodle strings absorb the moisture more than necessary, and the moisture is quickly removed from the noodle strings in the subsequent drying step, the noodle strings foam excessively and their structures become rough, and therefore, the noodle strings lose texture soon by boiling (see paragraphs 0007 and 0008 in PTL 3).
To solve this problem, PTL 3 describes that heated saturated steam is used in a steam atmosphere of a steaming step in the method for producing the instant noodles, an ambient temperature around the noodle strings is set to be higher than 100° C. and not higher than 125° C., and a time for the steaming step is set to about one to three minutes. PTL 3 describes that with this, it is possible to produce the instant noodles having smooth and elastic noodle quality and clear appearance without any surface roughness of the noodle strings, such as blisters or foaming.
In addition, proposed are to use the superheated steam for not the steam boiling but the drying of the food product (see PTL 4 for example), to adsorb a liquid containing brine water to a mass of the instant noodles subjected to the drying process and dry the mass again using the superheated steam (see PTL 5), and to throw the instant noodles subjected to the drying process into the superheated steam to give flexibility to the noodle strings and then compress and shape the mass (see PTL 6).